1.) A fail of such magnitude that it requires the ending "tastic"
2.) A fail that is larger than a Titanic Fail, but not quite a Catastrophic Fail
3.) A giant ass fail
4.) A fail so awesome, its almost a win.

Guy 1: Dude, did you see him slip on the skateboard and punch the kid in the throat?
Guy 2: Yeah man, that was so failtastic!
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Bro 1: Dude, did you see him get punched in the nuts by that girl?
Bro 2: Yeah! That was so failtastic I almost laughed!

Some one or something that has failed beyond reason and comprehension, so much so that the only way to describe the failure dealt would have to include the word fail and imply total and utter success at failing. Failing of this nature is like getting the gold medal of the fail olympics.